The lone term goals of this research is to understand the molecular basis and mechanism of regulation of a Ca2+ influx pathway referred to as capacitative Ca2+ entry (CCE2+), receptor operated Ca2+ channels (ROC) or store operated Ca2+ channels (SOC). CCE is a form of Ca2+ entry that is activated subsequent or concurrent with activation of phospholipase C in response to agonist occupancy of receptors that are either couped by the Gq or Gi families of G proteins or that mediate their effects through tyrosine phosphorylation. During the last two years we have followed the trail of a fruit fly mutant called transient receptor potential (trp) with properties consistent with having lost a CCE type channel. Several novel mammalian homologs have been cloned and we showed that one of them can increase CCE when expressed in a model cell, the COS cell. Moreover, mammalian trp antisense sequences interfered with a form of the mammalian CCE. Research proposed in this application is designed to define the molecular structure of CCE channels by describing further the molecular diversity of trp subunits and carrying out structure-function studies, by studying the subunit structure of CCE channels, and by defining their transmembrane topology. We also propose to explore possible mechanisms of CCE regulation, such as phosphorylation, vesicle translocation and interaction with other proteins. Finally, to gain further insight into the importance of trp proteins and be able to study them in isolation we propose to derive knockout mice for each of the known trp genes.